JPH0355069B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a speaker phone transmitting/receiving circuit for a telephone that enables simultaneous two-way conversation using amplified sound.

[Prior Art] Telephones with a loudspeaker calling function are a means of making calls that have many advantages, such as allowing a large number of people to participate in a call even when the user's hands are not on the phone.

However, until now, this type of telephone (speaker phone) has been put into practical use with an alternate call system.

This is because when a speaker and a microphone that are close to each other are driven at the same time, acoustic coupling occurs between the speaker that emits received information and the microphone that receives transmitted information, resulting in so-called howling. It is.

In other words, since both the transmitting system and the receiving system are turned on during a simultaneous two-way speakerphone call, the receiving signal output from the speaker is always input to the microphone, and this is transmitted again as a transmitting signal to the other party as an echo. Furthermore, due to the loss of balance in the balancing network circuit, the transmitting signal is output from the speaker (sidetone), and both of these causes a significant deterioration of speech quality as howling in a broad sense.

For this reason, in the speaker phones that have been put into practical use so far, the transmission and reception system is currently changed to a so-called half-duplex communication system or a pseudo-duplex communication system, as described above.

However, these technical means completely lose the excellent advantage of the inherent full duplex communication system of telephone lines. The conversation is
By nature, simultaneous bidirectionality allows even subtle differences in nuance to be conveyed between callers.

Therefore, the following proposals have been made as speakerphones capable of simultaneous two-way conversation.

That is, a slit is provided in the connecting surface between the speaker room and the sub-microphone room, so that the sub-microphone can receive the acoustic signal from the speaker through this slit.

(b) The audio signals input from the speakers to the main microphone and sub microphone are input to the operating amplifier, the in-phase components of both signals are removed to prevent howling, and only the voice of the caller is transmitted from the main microphone. .

[Problems to be Solved by the Invention] However, the above conventional technology has the following problems.

(b) Providing a submicrophone increases the cost and complicates the circuit.

(b) A sub-microphone chamber must be formed in the housing, which complicates the structure of the housing and makes it difficult to design and manufacture.

C. It is necessary to provide a separate power supply to drive the operating amplifier, which increases costs.

The present invention has been made in view of these problems, and it is an object of the present invention to provide a transmitting/receiving circuit for a speakerphone for a telephone that can prevent howling from occurring with an inexpensive and simple configuration.

[Summary of the Invention] The present invention provides a telephone in which a speaker and a pair of microphones are housed in the same housing.
a first microphone arranged so that an acoustic signal from the speaker can be inputted through the housing member;
A second microphone is arranged so that a voice transmission signal and an acoustic signal from the speaker can be inputted through air propagation, and after inverting the phase of the input signal of the second microphone, the input signal is input to the first and second microphones. In a transmitting/receiving circuit of a telephone speakerphone having a transmitting circuit section that cancels signals and then sends them out via a high-pass filter, the receiving signal from the line and the transmitting signal from the high-pass filter of the transmitting circuit section. a first filter that removes high and low frequencies of the transmission signal; a second filter that removes the low frequencies of the transmission signal from the high-pass filter; and a phase control circuit that inverts the phase of the output signal of the second filter. and an output circuit unit that mixes and cancels the output signals of the phase control circuit and the first filter, and then outputs the output signals from the speaker as an acoustic signal, the transmitting signal component included in the output signal from the first filter being output from the speaker. By removing the noise and outputting it to the speaker, it is possible to improve the sound received from the speaker.

[Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described based on the drawings.

FIG. 1 is an overall circuit diagram showing a schematic configuration of an embodiment of a transmitting/receiving circuit of a telephone speakerphone according to the present invention.

In the figure, A indicates a first microphone 1, a second microphone 2, a phase control circuit 3 as a first phase control means, a non-inverting amplifier 4, a variable resistor 5 as an adjustment mixing means, and a high-pass filter. 7
a. This is a transmitting circuit section consisting of an inverting amplifier 6 and outputting a transmission signal to the destination.

B is an output circuit that is composed of a first filter 8, a second filter 7b, a power amplifier 9, a phase control circuit 16, an automatic gain control (AGC) 10, a speaker 11, etc., and outputs a reception signal from the other party. Department. 12 is a speech network IC that separates the received signal and the transmitted signal;
13 is a balancing network for 2-wire to 4-wire exchange, and 14 is a diode bridge.

In the above configuration, the second filter 7b
uses one that is effective for low frequencies. Further, the first filter 8 is a bandpass filter, which is effective for low and high frequencies.

FIG. 2 is an external perspective view of a housing 17 that houses the first microphone 1, second microphone 2, speaker 11, etc. The first microphone 1 transmits only the acoustic signal from the speaker 11 into the interior of the housing 17 so that the acoustic signal is input into the housing 17 itself as a propagation means, the air propagation within the housing 17, and the housing itself is input as a propagation means. Directly attached.

A second microphone 2 into which a transmitting signal is input
is completely acoustically shielded by a shielding plate 2a within the housing 17, and the speaker 11
The acoustic signal from the housing 17 is input only by air propagation outside the housing 17.

Next, the operation of this embodiment will be explained.

The acoustic signal from the speaker 11 is input to the first microphone 1 using a housing material or the like as a propagation means, and is converted into an electric signal (reception signal) and input to the phase control circuit 3, where the phase shift is detected. It is corrected and also inverted by 180° to the non-inverting amplifier 4.
The signal is input to one end of the variable resistor 5 via.

On the other hand, the second microphone 2 receives a transmission signal from the speaker and an acoustic signal from the speaker 11, and outputs the mixed electrical signal. Then, the mixed transmitting/receiving signal is adjusted by the amplifier 6 to approximately the same level as the receiving signal from the speaker 11 which is input from the first microphone to the variable resistor 5, and then output. Furthermore, the respective output signals from the first and second microphones input to both ends of the variable resistor 5 are completely balanced in level by the operation of the variable resistor 5, cancel each other out, and are sent. Only speech signals are extracted.

The transmission signal taken out from the variable resistor 5 is further input to a filter 7a, where unnecessary high band components are removed, and then sent to the speech network 1.
It is sent to the line via 2nd etc.

On the other hand, the filter 8 of the output circuit section B receives a signal that is a mixture of the receiving signal from the called party and the transmitting signal from the transmitting circuit section A that has passed around to the output circuit section B due to the sidetone effect. is input. This filter 8 is a bandpass filter, and unnecessary high and low frequency components are removed from the mixed signal by this filter 8.

Further, the transmitting signal outputted from the filter 7a is outputted to the filter 7b, unnecessary low frequency components are cut out, and only necessary middle and high frequency band components are inputted to the phase control circuit 16. .
Then, in the phase control circuit, after adjusting the phase of the input transmission signal, the phase is further inverted by 180° and mixed with the transmission and reception mixed signal output from the filter 8 described above. Here, phase control circuit 1
The level of the anti-redirected speech signal outputted from the filter 8 and the level of the transmitted speech signal component included in the mixed transmitted and received speech signal outputted from the filter 8 are approximately determined by the variable resistor 15 inserted between the filters 7a and 7b. Since they are set to be the same, the transmitting signal component included in the mixed transmitting and receiving signal is canceled out by the anti-transferring signal output from the phase control circuit 16.

Note that the levels of the transmitted voice signal and the counter-transferred voice signal that are canceled out in this manner can be adjusted by adjusting the variable resistor 15. That is, since the transmitted speech signal component sent from the filter 8 and the anti-transferred speech signal outputted from the phase control circuit 16 have different signal path frequency characteristics, etc., the variable resistor 15 must be adjusted. Each of them changes by drawing a different curve. Therefore,
By setting the resistance value of the variable resistor 15 at the point where each curve intersects, the levels of both signals can be matched.

As a result of the above, the speaker 11 is prevented from being inputted with the transmission signal that goes around to the output circuit section due to the collapse of the balancing network (B/N), and the output signal is within the required medium and high frequency band. Only the received signal components of are input. Therefore, the speaker can output only a good received voice that does not include transmitted voice or noise.

In addition, since only the proper received voice sound as described above is output from the speaker 11, the cancellation and removal of the received voice sound in the transmitting circuit section can be performed appropriately.
The occurrence of howling can be reliably suppressed.

Furthermore, in this embodiment, the signal input to the speaker 11 is transmitted to the auto gain control circuit 1.
0 to the level of the proper range, i.e. the first
Since the receiving signal has a level within a range where it is easy to cancel out each signal output from the second microphone, a better howling prevention effect can be obtained.

[Effects of the Invention] As described above, according to the present invention, the occurrence of howling can be appropriately prevented in a simultaneous two-way communication system using loudspeaker, and good communication performance can be obtained. By specifying the range to be necessary and sufficient for a telephone call, it is possible to make a telephone call using only the line power supply, which also has the effect of making it possible to use the system at low cost.

[Brief explanation of drawings]

FIG. 1 is an overall circuit diagram showing a schematic configuration of an embodiment of the present invention, and FIG. 2 is an external perspective view of the housing. A... Transmission circuit section, B... Output circuit section, 1...
1st microphone, 2...Second microphone, 3...Phase control circuit, 7a...High frequency filter, 7b...Second filter, 8...First filter, 10...AGC circuit , 11... Speaker, 16... Phase control circuit.

Claims (1)

[Scope of Claims] 1. A telephone in which a speaker and a pair of microphones are housed in the same housing, and the first microphone is arranged so that an acoustic signal from the speaker can be inputted through the housing member, A second microphone is arranged so that a voice transmission signal and an acoustic signal from the speaker can be inputted through air propagation, and after inverting the phase of the input signal of the second microphone, the input signal is input to the first and second microphones. In a transmitting/receiving circuit of a telephone speakerphone having a transmitting circuit section that cancels signals and then sends them out via a high-pass filter, a receiving signal from the line and a transmitting signal from the high-pass filter of the transmitting circuit section are provided. a first filter that removes high and low frequencies of the transmission signal; a second filter that removes the low frequencies of the transmission signal from the high-pass filter; and a phase control circuit that inverts the phase of the output signal of the second filter. and an output circuit unit that mixes and cancels the output signals of the phase control circuit and the first filter, and outputs the resultant sound signal from the speaker as an acoustic signal, the transmitting signal component included in the output signal from the first filter being output from the speaker. A transmitting/receiving circuit for a speakerphone for a telephone, characterized in that the signal is removed and the signal is output to the speaker.